Distillation and chromatography

Classroom resources

Load these into Waypoints Prepare: choose Load URL and paste the copied address, or download the file and import it. In Prepare, the worksheet's Teacher edition shows the answers; the student copy hides them.

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• Worksheet Download Copy address for Prepare Print the student copy; the Teacher edition has the answers.

Students will be able to

• I can describe the principle of distillation and of chromatography.
• I can name a mixture each technique suits.
• I can explain when distillation is used instead of evaporation.

Timing

Engage and Explore 10 min · Explain 8 min · Evaluate 3 min · Typical adds 4 min, Wider about 15 min

Before class

A concept tutorial for introducing or revising the techniques. Set the width with ?width=minimum, typical (default) or wider.

The node's response mode is structured reasoning: students confuse distillation with evaporation because both heat a liquid. The Explain sort scaffolds the comparison row by row.

First Nations content: the node file lists steam distilling among First Nations techniques. This tutorial does not claim that. It presents documented traditional tea tree use (crushing and soaking leaves) and makes clear that steam distillation is the modern extraction method. Check with local community knowledge and protocols, and adapt to the Country your school is on.

Running the lesson

1. Engage: most students predict salty water. Watch the board together to see only water particles cross.
2. Explore: chromatography is quick to run for real with felt-tip pens, filter paper and water; do it if you can.
3. Explain: read the sort aloud as a comparison table: same property, different outcome, different equipment.

The hard part (on purpose)

Explaining each technique by the property it uses. When a student says distillation is just evaporation, ask what happens to the steam in each.

When students get stuck

Answers to the checks

1. Engage: fresh water from seawater: Seawater is heated in a flask. A tube carries the steam through a cold jacket into a second, empty flask. What collects in the second flask?
   Fresh water. Only water particles boil off; the salt stays behind in the first flask.
2. Distillation: Distil the seawater until the first flask is dry.
   
3. Chromatography: Run the chromatography.
   
4. Which pen?: Which pen wrote the note?
   Pen B
   Pen B's dyes match the note's exactly. Pen A has an extra red dye.
5. Compare: Both techniques heat a liquid until it turns to gas. Sort each statement.
   Uses the difference in boiling point → Both; Needs heat → Both; The vapour escapes into the air → Evaporation only; The vapour is cooled and collected as a liquid → Distillation only; You end up with only the solid → Evaporation only; You end up with the liquid and the solid → Distillation only; Needs a condenser and a collecting flask → Distillation only
   Same property, different outcome: distillation keeps the vapour by cooling it.
6. The dyes: Why do the dyes in the ink end up at different heights?
   Each dye dissolves in the water and sticks to the paper differently, so the water carries each one a different distance
   Dyes that dissolve well and stick weakly travel furthest.
7. Which technique suits?: Match each job to the technique that suits it.
   Get drinking water from seawater → D. Distillation; Get salt from seawater, letting the water go → C. Evaporation; Find out which dyes are in a black ink → A. Chromatography; Get sand out of sandy water → B. Filtration
   Need the liquid back? Distil. Need only the dissolved solid? Evaporate. Several dissolved substances, such as dyes? Chromatography.
8. Mix it up: Looking back at heating curves: water in a flask is boiling and the heat stays on full. What does a thermometer in the water show over the next few minutes?
   It stays at about 100 °C
   During a change of state the temperature stays the same: the energy goes into pulling the particles apart into steam.
9. Elaborate: distillation or evaporation?: Both use the same property. Which would you choose?
   A salt farm wants salt from seawater. → Evaporation; A ship needs drinking water from seawater. → Distillation; A lab wants very pure water with nothing dissolved in it. → Distillation; You want sugar crystals from sugar syrup. → Evaporation; You want to keep both the water and the salt from a salt solution. → Distillation
   Ask: do I need the liquid? If yes, distil.
10. Elaborate: three techniques, three properties: Which property does each technique use?
    Crystallisation: a hot, concentrated solution is left to cool, and crystals form. → How much solid can stay dissolved; Chromatography: food colourings separate on paper. → How well each substance dissolves and sticks to the paper; Distillation: alcohol is separated from water. → Boiling point
11. Elaborate: First Nations knowledge and plant oils: Which property or process does each step use?
    Crushing tea tree leaves → Breaking up the leaves so substances can get out; Soaking crushed leaves in water → Some substances dissolve in water; Modern steam distillation: steam passes through the leaves → The oil is carried away with steam, then condensed; Modern steam distillation: separating the collected liquid → The oil floats on the water
12. Blue: The blue spot moved 8.0 cm. What is its Rf value?
    0.8
    8.0 ÷ 10.0 = 0.80
13. Red: The red spot moved 5.0 cm. What is its Rf value?
    0.5
    5.0 ÷ 10.0 = 0.50
14. Unknown dye: An unknown dye has Rf = 0.50 in the same setup. Which dye could it be?
    The red dye
    Same Rf value, same conditions: probably the same substance.
15. One spot: A green ink gives just one spot. What can you conclude?
    It is probably one dye, but two dyes with the same Rf value would also give one spot
    Testing again with a different solvent would check.

Stretch and support

Stretch: Why does salt not travel through the condenser with the water? Use particle motion and boiling points.

Support: Give the comparison as a table with two columns, evaporation and distillation, to fill in before the sort.

Coach prompt (optional)

For a student who has done the lesson and is still stuck. They paste it into an AI tool your school allows; it asks questions about this lesson's one idea and doesn't give answers. Students see it on the course recap page only through a link ending in ?coach=1: recap with coach prompts.

You are a patient science coach for a Year 7 student in Australia. Help me understand ONE idea only, from the lesson "Distillation and chromatography".

The idea: Distillation and chromatography: I can describe the principles of distillation and chromatography and identify mixtures each technique is appropriate for.

What understanding looks like:
- Describes the principle of distillation and chromatography
- Identifies a mixture appropriate for each technique
- Distinguishes when distillation is preferred over evaporation

Mistakes students often make here:
- A student says distillation and evaporation are the same.
- A student says the heavier dyes stay lower.
- A student thinks black ink is a single substance.

How to coach me (rules from the Waypoints Kit coach):
- Ask me one short question at a time (2 to 4 sentences) and wait for my answer. Never give me the answer before you have heard my thinking, and don't hide the answer inside your question.
- Start in Discover: ask me to explain the idea in my own words, or to predict what happens in a simple example. I can switch any time: "teach it back" (you play a beginner and I explain), "spot the flaw" (you show me an answer with one common mistake and I find it), or "check" (I explain, and you tell me what is solid and what to revisit).
- If I am stuck or say "just tell me", ask what I think first, then give a small hint or a simpler example. Explain only after I have had a real go.
- If I seem to be missing the idea that comes before this one (Filtration and evaporation), check it quickly, then come back.
- Stay in this idea: don't teach later ideas or add extra content. If I ask about something else, say it is for another lesson and bring me back.
- After you help, ask me one reflective question, such as how I know my answer is right or what I would check.
- Praise my effort and method, not my ability.
- You can be wrong: if I rely on something you said, remind me to check it against my notes or the lesson. If you don't know, say so.
- Use simple words.
- Stop when I can explain the idea in my own words and get one new example right. Then tell me to go back to the lesson "Distillation and chromatography".

Exit ticket

Why would a ship use distillation, not evaporation, to get drinking water from seawater?

Distillation collects the water vapour as liquid; evaporation lets it escape and keeps only the salt.

What each step is for

• Engage: fresh water from seawater: Predicting the collected liquid sets up the key difference from evaporation: the vapour is kept.
• Explore: run both techniques: Watching single particles travel through the condenser makes 'collect the vapour' concrete; the chromatogram shows black ink is a mixture.
• Explain: distillation is not just evaporation: The node's response mode is structured reasoning: compare the two techniques feature by feature (same property, different outcome, different equipment).
• Mix it up: The flat part of a heating curve explains why boiling water holds a steady temperature, which is what the flask in a distillation is doing.
• Elaborate: distillation or evaporation?: The choice depends on what you want to keep: if you need the liquid, distil.
• Elaborate: three techniques, three properties: Crystallisation, chromatography and distillation each use a different property.
• Elaborate: First Nations knowledge and plant oils: Traditional and modern methods of getting substances out of plants both rely on property differences.
• Elaborate: reading a chromatogram: Rf values turn a chromatogram into evidence, and a single spot is evidence, not proof.

Where it leads

Next in class: AC9S7U06 node 5, choosing and justifying a technique for a new mixture, works best as a class task.

Practical: paper chromatography of felt-tip pens or food colourings; a demonstration distillation of coloured water.